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https://issues.apache.org/jira/browse/HDFS-17342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17808880#comment-17808880
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ASF GitHub Bot commented on HDFS-17342:
---------------------------------------
haiyang1987 commented on code in PR #6464:
URL: https://github.com/apache/hadoop/pull/6464#discussion_r1460291058
##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java:
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@@ -2416,11 +2419,21 @@ public void invalidateMissingBlock(String bpid, Block
block) {
// So remove if from volume map notify namenode is ok.
try (AutoCloseableLock lock = lockManager.writeLock(LockLevel.BLOCK_POOl,
bpid)) {
- ReplicaInfo replica = volumeMap.remove(bpid, block);
- invalidate(bpid, replica);
+ // Check if this block is on the volume map.
+ ReplicaInfo replica = volumeMap.get(bpid, block);
+ // Double-check block or meta file existence when checkFiles as true.
+ if (replica != null && (!checkFiles ||
+ (!replica.blockDataExists() || !replica.metadataExists()))) {
+ volumeMap.remove(bpid, block);
+ invalidate(bpid, replica);
Review Comment:
`If replica == null` should not need to execute `invalidate(bpid, replica)`
avoid cause NPE.
> Fix DataNode may invalidates normal block causing missing block
> ---------------------------------------------------------------
>
> Key: HDFS-17342
> URL: https://issues.apache.org/jira/browse/HDFS-17342
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Haiyang Hu
> Assignee: Haiyang Hu
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.5.0
>
>
> When users read an append file, occasional exceptions may occur, such as
> org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: xxx.
> This can happen if one thread is reading the block while writer thread is
> finalizing it simultaneously.
> *Root cause:*
> # The reader thread obtains a RBW replica from VolumeMap, such as:
> blk_xxx_xxx[RBW] and the data file should be in /XXX/rbw/blk_xxx.
> # Simultaneously, the writer thread will finalize this block, moving it from
> the RBW directory to the FINALIZE directory. the data file is move from
> /XXX/rbw/block_xxx to /XXX/finalize/block_xxx.
> # The reader thread attempts to open this data input stream but encounters a
> FileNotFoundException because the data file /XXX/rbw/blk_xxx or meta file
> /XXX/rbw/blk_xxx_xxx doesn't exist at this moment.
> # The reader thread will treats this block as corrupt, removes the replica
> from the volume map, and the DataNode reports the deleted block to the
> NameNode.
> # The NameNode removes this replica for the block.
> # If the current file replication is 1, this file will cause a missing block
> issue until this DataNode executes the DirectoryScanner again.
> As described above, when the reader thread encountered FileNotFoundException
> is as expected, because the file is moved.
> So we need to add a double check to the invalidateMissingBlock logic to
> verify whether the data file or meta file exists to avoid similar cases.
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